The present invention relates to improved devices for supporting equipment in a well, such as an oil or gas well.
In prior art wellhead arrangements, it is known to suspend tubing from a coupling, which in turn is supported on an inwardly facing, frusto-conical surface of a suspension nut. The frusto-conical surface is positioned radially inwardly of and axially aligned with an outer threaded surface of the nut, which is made up on the threads of a tubing head adapter at the wellhead. The threads fit closely together; accordingly, the suspension nut is made relatively thick, ensuring that it will not expand significantly outwardly.
The threads of the suspension nut are required to support the tubing when it is reciprocated upwardly from the tubing head (for example, to pull out of a packer). Also, it often happens in many wellhead assemblies that the threads alone must support the nut and the tubing string, even when it is not being reciprocated. If the nut backs out, this will result in dropping a tubing string which typically is several thousand feet long, with potentially significant damage. It can also result in loss of control over downhole pressures. However, because the suspension nut is enclosed between the tubing and the tubing head adapter, it is difficult to utilize conventional means, such as a set screw, to prevent the threads from backing out.